The present invention relates to a mobile machine and in particular deals with the enormous ground pressure obtained under the load of a mobile machine, for example a crawler crane.
The high ground pressure obtained under the load of a mobile machine is regarded as a decisive factor which is to be clarified prior to an operation of a mobile machine. In particular with a boom orientation of a crawler crane which is parallel to the longitudinal direction of the undercarriage or deviates therefrom by the angular amount of +/−30°, ground pressures occur which are two to three times as large as is the case with a boom orientation transversely to the undercarriage (and thus also transversely to the crawler supports). In extreme cases, ignoring or underestimating this high pressure variation or also the high ground pressures in general leads to accidents due to ground failure. In this case, the ground present under the crawler crane yields due to the too high ground pressure and in the unfavorable case makes the crawler crane tilt towards one side.
The high supporting pressure exerted on the ground by the crawler crane is due to the geometry of the tracklaying gear. In the two crawler supports aligned parallel to each other, the entire standing surface of the crawler is loaded uniformly in the case of a load acting transversely to said crawler supports (sidewards). In the case of a load acting longitudinally with respect to the crawler supports (forwards), no uniform, but a trapezoidal or triangular ground pressure distribution is obtained, which depends on the location of the center of gravity or center of pressure of the crawler crane. When the eccentricity of the center of pressure is greater than one sixth of the crawler standing surface, this even leads to the fact that a part of the standing surface of the crawler lifts off, which leads to a further increase of the maximum ground pressure. Such situation typically is obtained in the case of a large load moment with forwardly directed boom.
To avoid tilting of the crawler crane, considerations are made in the prior art to provide foldable support arms which increase the stability of the crane during the operation (cf. US 2010/0320166 A1 or CN 2308636 Y). Typically, the crawlers lift off with extended support arms, in order to prevent an undefined flux of force which depends on the rigidities of the support arms and the supporting structure or the crawler supports. In this implementation it is disadvantageous that the construction variants proposed in the prior art are very costly and expensive. In addition, the entire weight of the undercarriage is increased considerably, which involves additional disadvantages with regard to the transport and the assembly time of the crane. Moreover, the support arms protruding to the outside from the crawler crane require additional space, which is not easily available at any site of use.